Wheel loaders are often equipped with a shovel actuated via a power takeoff (PTO) of the power shift transmission, for example, for filling and emptying or conventional power shift transmission of wheel loaders keep the power shift clutch closed while filling and emptying the shovel or “when operating on the wall” and thus a large part of the input power becomes heated in the torque converter. To overcome said disadvantage, it is known to open the power shift clutch starting from a specific brake pressure upon the service brake in order that the torque converter does not absorb any more power and all the input power goes to the power takeoff of the power shift transmission of the wheel loader. One disadvantage here is that there is absolutely no more propelling force on the wheels of the wheel loader, since there has been an active deceleration and in addition no more gear is shifted when the power shift clutches are disengaged.
PCT/EP 95/01520 has disclosed a device for reducing the pressure of a power shift clutch used in transmission systems for working machines. In this prior art, a pressure-reducing valve is used to make a power shift clutch slip in the transmission so that the working machine moves slowly and, for example, can be moved exactly to a specific position. A relation to the requirements on wheel loader while filling/emptying the shovel or “when operating on the wall” is not to be understood from PCT/EP 95/01520.
The problem on which the invention is based is to provide a control of a drive train which assists a wheel loader during filling and emptying “when operating on the wall” overcoming the disadvantages of lack of propelling force on the wheels.